An optical device having an optical element, such as a light emitting element or a photoelectric conversion element, formed on a substrate includes a transparent electrode made of a light transmissive conductive material. Since the light transmissive conductive material is generally high in resistance, the transparent electrode would also be high in resistance. Therefore, in order to lower the resistance of the transparent electrode, the transparent electrode is sometimes provided with an auxiliary electrode, as illustrated in Patent Document 1, for example. In Patent Document 1, the auxiliary electrode is formed on the transparent electrode and covered by an insulating film. Patent Document 1 also discloses inkjet printing as one of the methods of forming the auxiliary electrode.